With the development of wireless communications technologies, in order to satisfy requirements of the International Mobile Telecommunication Advanced (IMT-Advanced) and to support a peak data speed being up to 1G, a Long Term Evolution system currently uses a carrier aggregation technology as a method for expanding a system bandwidth. Carrier aggregation mainly aggregates multiple component carriers into one carrier higher than 20 million hertz (MHz) to support high data transmission speed.
Currently, an LTE or Long Term Evolution-Advanced (LTE-A) system needs to support asymmetric carrier aggregation. Generally, the number of downlink component carriers is greater than the number of uplink component carriers. For example, a downlink bandwidth of 80 million hertz (MHz) includes four component carriers of 20 MHz. An uplink bandwidth of 20 MHz includes one component carrier of 20 MHz.
In the current LTE system, in a handover process, a non-competitive procedure for a User Equipment (UE) to randomly access a target eNB includes the following steps.
The UE sends a measurement report to a source eNB, and the source eNB selects a target eNB and a target cell for the UE according to the received measurement report or other radio resource information, that is, the source eNB makes a handover decision. Then, the source eNB sends a handover request message to the target eNB. After receiving the handover request message, the target eNB executes admission control and feeds back a handover request acknowledgement message to the source eNB. When receiving the handover request acknowledgement message, the source eNB sends a handover command message to the UE. After the UE receives the handover command message, if the UE receives a dedicated random access preamble allocated by the target eNB to the UE, the UE sends a random access request message to the target eNB through the dedicated random access preamble, that is, the UE executes non-competitive random access; if the UE does not receive the dedicated random access preamble allocated by the target eNB to the UE, the UE executes competitive random access. After receiving the random access preamble sent by the UE, the target eNB sends a random access response message to the UE.
However, the inventor of the present invention finds that, in the foregoing process, when the target eNB includes multiple component carriers, after the target eNB receives the random access request message, the target eNB cannot determine the component carrier which the UE is monitoring, in order to enable the UE to receive the random access response message, the target eNB needs to send the random access response message on all component carriers, thereby resulting in a waste of downlink resources.